title: Effect of pH on methylene blue transient states and kinetics and bacteria photoinactivation.
abstract: We have measured directly by time-resolved spectroscopy the transient spectra and kinetics of the methylene blue (MB) excited singlet and triplet state as a function of pH from a few picoseconds to several microseconds. The data show that the acidic triplet state (3)MBH(2+) is the protonated analogue of the basic (3)MB(+). It is also shown that the singlet oxygen formation quantum yield is much higher in basic than in acidic media. The transient spectra and their kinetics suggest that because pH exerts a large influence in singlet oxygen and radical formation, it may also be important in bacteria inactivation. Therefore, we performed experiments, which showed that the rate of gram-positive and gram-negative bacteria inactivation at pH 9 is 3-25 times higher than the rate at pH 5.
authors.affiliation: Key Laboratory for Laser Plasmas (Ministry of Education) and Department of Physics, Shanghai Jiao Tong University, Shanghai, 200240, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Cesario
authors.forename: Peter M
authors.initials: PM
authors.lastname: Rentzepis
mesh_terms: D001419:Bacteria / Q000737:chemistry / Q000378:metabolism*; D018407:Bacterial Physiological Phenomena; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008751:Methylene Blue / Q000737:chemistry* / Q000378:metabolism*; D010777:Photochemistry; D026082:Singlet Oxygen / Q000737:chemistry*
chemical_list: D026082:Singlet Oxygen; D008751:Methylene Blue